A crosslinked resin can be obtained by crosslinking a thermoplastic resin with a crosslinking agent such as an organic peroxide. The demand for crosslinked resins as a circuit substrate insulation material used in electrical devices, especially communications, computers and the like, is increasing. A circuit substrate insulation material needs to have a low relative permittivity and heat resistance to withstand use for high density wiring. Various proposals have been made to respond to these needs.
For example, Patent Literature 1 discloses a polymerizable composition comprising a norbornene monomer, a metathesis polymerization catalyst, a chain transfer agent and a crosslinking agent. According to Patent Literature 1, this polymerizable composition has fluidity, and can thus be soaked into a support medium made of nonwoven fabric or the like or be molded into a film form. A crosslinkable thermoplastic resin can be obtained by carrying out bulk polymerization of this polymerizable composition. Further, Patent Literature 1 also discloses that various crosslinked resin composites can be obtained by laminating this crosslinkable thermoplastic resin on a substrate such as a metal foil, and crosslinking the laminate.
Patent Literature 1 International Publication No. WO2004/003052
Patent Literature 2 discloses an electrical insulation material in which air bubbles or air chambers are enclosed in a dicyclopentadiene resin. Patent Literature 2 discloses that this electrical insulation material is obtained by blending a metathene monomer, a ruthenium complex catalyst, and plastic balloons, and curing the resultant mixture.
Patent Literature 2 Japanese Patent Laid-Open No. 2004-63326
Patent Literature 3 discloses a resin composition in which fine hollow glass spheres having a ratio of shell wall thickness to particle size of 1/6 to 1/11 are mixed in a thermosetting resin. Patent Literature 3 teaches that a prepreg can be obtained by impregnating this resin composition in a substrate, and drying the impregnated substrate. As the thermosetting resin, Patent Literature 3 discloses a thermosetting polyimide resin which contains a diamine and bismaleimide as main components.
Patent Literature 3 Japanese Patent Laid-Open No. H06-65407